Numerous different types of props have been proposed and manufactured heretofore and, most of the inexpensive or relatively inexpensive props have been made of wood.
Prop designers aim to produce a prop which will yield when it initially accepts a compression load and which has a steadily increasing resistance to such yield but which remains stable and continues to support a load after yielding.
An early proposal was to sharpen the end of a wooden pole so that a pointed end initially supported the load. As the load increased, the point was flattened so that the load acted on a continuously increasing area of the pole. Such poles had improved characteristics when compared with plain poles with unshaped ends, but still left a lot to be desired so far as load bearing capability was concerned.
Various other attempts have been made to manufacture effective and yet inexpensive timber props and these attempts vary widely in their approach and construction. One of the most important and effective props manufactured to date consists of a turned or otherwise rounded pole located tightly within a ductile metal pipe acting as a sleeve. In use this prop can contract under compressive loads and in fact, when the length thereof has been shortened to a certain extent, the pipe or sleeve can deform outwardly to accept the displaced bulk of the wood composition.
Another proposal has been to encase a pole within a sheath of glass fibre reinforced epoxy resin material with the same ultimate end in view.